what would be bad is the vacuum leak at idle.

 

But I mean....it would be at idle. I dont see what would be wrong, as long as it doesnt leak when you throttle it...Right? Or would it give a lag

 

the whole point is to reduce the amount of boost into the wastegate.

say the wastegate opens at 7psi. a way to control that is to reduce the amount of boost the wastegate sees. If you bleed the boost to just the wategate it won't open at 7psi because you've reduced the amount of boost in just that small section of vacuum line. When you adjust the amount of leak, you control the level of boost.

the check valve ensures that when you are idling or cruising you do not have a vacuum leak, as that will screw up your AFR. In boost, the very small amount of boost you are bleeding off does little/nothing.

 

Ohh Ok. I somewhat understand that. Thanks again.

 

typically people now use the ball-and-spring MBC:



the idea here is keeping the wastegate closed as long as possible to increase spool, all while being able to maintain control of your boost level.

the way it works is completely sealing the boost from entering the wastegate. keeping the wastegate shut helps increase your spool-up rate. the bleed-type MBC always allows some boost to slightly open the wastegate more and more adversly affect spool.

you set your boost level by the pre-load on the spring inside the MBC. once the boost overcomes that pre-load then ball lifts out of the way and boost will enter the wastegate and it will open the flapper.

 

The piece in the last post looks easy enough to make from various Home Despot parts.

I assume the in comes from the turbo and the out goes to the wastegate?

What sort of spring do you end up using? Is there a measure for tension that it holds? Am I thinking about this too much?

 

My bad, found this by searching some more.

http://www.geocities.com/chmwatson/FAQs/mbc.html